Hadith 8:34
Abu Qatada reported God’s Messenger as saying, “Avoid much swearing while transacting business, for it produces a ready sale then blots out the blessing.” Muslim transmitted it.
وَعَنْ أَبِي قَتَادَةَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ «إِيَّاكُمْ وَكَثْرَةَ الْحَلِفِ فِي الْبَيْعِ فَإِنَّهُ يُنَفِّقُ ثُمَّ يَمْحَقُ» . رَوَاهُ مُسلم
Original Reference: Mishkat al-Masabih 2793